Television system



Feb. 6, 1934. J. L.. BAIRD 1,945,626

TELEVI S ION SYSTEM Filed Jan. 6, 1928 Patented Feb. 6, 1934 UNITED STATES PATENT OFFICE TELEVISION SYSTEM Application January 6, 1928, Serial N0. 244,963,

and in Great Britain January 26, 1927 10 Claims.

'Ihis invention relates 1:0 the transmission of signals for television and like purposes, and has for its object to provide an improved method of and apparatus for such transmission.

It is advantageous from the point of view of speed of transmission that a picture o1" view should be explored in a number of different sections simultaneously, but heretofore the transmission of the signals ari sing from such simulta neous explorations has necessitated a corresponding number of lines in the case cf wired transmission, or of separate wave-lengths for wireless transmission.

This invention accordingly comprises in a television system, the method of transmitting a plurality of individual signals consisting in recording them simultaneously or in concurrent groups on a record-element er elements and therea fter reading all the individual records in succession (for example, at a higher speed) by a device which is operatively connected to the transmitter. y

According to another feature 0f this invention, the reading device may have associated with it means for wiping out the record which has just been read, so that a fresh record may be ma de immediately thereafter.

According to another feature of this invention it consists in exp1oring simultaneously various sections cf a picture or view to be transmitted, recording the groups of signals corresponding to each section of the picture on a record element and traversing the record thus formed by a device which reads the record and transmits the signals to the receiving station.

A similar but reversed arrangement may be used at the receiving station, the signals being transmitted successively at, say, a high rate, and recorded on an element or group cf e1ements, such signals being thereafter read simultaneous- 1y in groups on different parts of the record.

This invention also covers certain details of the apparatus as hereinafter described.

In the accompanying drawing- Figure 1 is a diagram'matic representation of one form of apparatus suitable for carrying out the present invention;

Figures 2 and 3 are diagrammatic representations of alternative forms of apparatus.

Referring first to Figure 1, which illustrates diagrammatically a construction of apparatus in which magnetic recording is used, there is provided a series of discs 40, 41, 42 of. steel or other suitable magnetic material mounted on a. shaft 43 which is arranged to be rotated at any suitable speed. The number of discs is equal to the number of sections in which the picture is explored, and one disc is appropriated to each section.

It will be understood. that any suitable means adapted to explore several sections of an image simultaneously may be used for the purpose. F01 instance, a plurality of separate exploring devices may be used, each positioned so as to scan one sectiononly cf the image. If preferred, an exploring device such as is shown in my copending application Serial N0. 244,964, fi1ed Jan. 6, 1928, in which a Single rotating disc is capable of' simultaneously exploring difierent sections of an image, may be utilized.

The signals derived from the light-sensitive or photoelectric cel1 for each section are applied respectively to magnetizing coi1s 44, 45 46, so as to make a corresponding record on each of the discs during its rotation. Each of the discs also has associated with it a search-coil, indicated at 47, 48 and 49, this coi1 being so mounted that it can be rotated in the opposite direction to the disc at a higher speed. Conveniently, when three discs are used, the searchcoil will rotate at twice the speed of ehe disc.

Each search-coil has associated with it a wiping-out-coil energized by alternating current of a suitable frequency, and this coil is rotated immediately behind the search-coil so that after a record has been read it is erased, and the recordelement is 1eft ready to receive a new record; these wiping-out-coils are indicated ab 50, 51, 52.

In the operation of this de'vice, t he records for the three sections cf the picture being transmitted are made concurrently and impressed upon the respective discs as record-elements. When the record on the first disc has been completed, as indicated diagrammatically by the 1ine 53, the search-coil 47 is connected in circuit so that on its next revolution from ehe position indicaced in Figure 1 it reads this record, and simultaneously erases it. Since this coi1 is rotating at twice the speed of the disc, it completes-the reading during one-third of a revolution cf the, disc, and is thereupon disconnected, and the search-coil 48 is connected in the transmitting circuit in its place. It then reads and transmits the record on thdisc 41, and on the conipletion thereof is disconnected, and the search-coil 49 reads and transxnits the record on the disc 42.

The record on the disc 40 was erased immediately after it was read, and the coi1 44 impressed a new record thereon, the recording commencing immediately after the reading of the previous record commenced and continuing whilst; all three records on the discs 40, 41, 20 are being read and transmitted. Since the search-coils rotate at twice the speed of the discs, the disc 40 will have had a 11111 record impressed upon lt by the time the search-coil 49 has finished reading the disc 42 so that the cycle of operations cf reading ehe three discs in succession can be repeated. In this way, therefore, the magnetizing cells are in operation practically continuously, and each search-coil is reading and transmitting a record for one revolution in three, so that the whole process of recording, reading and transmitting is a substantially continuous one, and the rate of transmission of the sei) of Signals constituting the complete picture (made up of the three sections) is three-times as great as it would be with a. single exploring and. transmitpting devlce.

In order to obtain a. cyclic series of operations, lt Will be seen that each search-coil in its rotation should meet the heacl end 01 the record lt is to read at an appropriate time, and the simultaneous records on the three disos, should therefore be started 120 apart. This is most readily effected4by selection of the position of the exploring disc for each sectlon.

Other arrangements of recording element may be used, such for example as is illustrated in Figure 2. In this case there is a single disc 10 01 steel or other suitable magnetio material mounted on a. shaft 11 which is arranged to be rotated at any suitable speed. The picture may be explored in three sections, and the exploring devioes are connected respectively to three magnetizing-coils 12, 13, 14, which are spaced apart around the periphery 01 the disc 10. In the particular arrangement illustrated, these coils are spaced 60 degrees apart around one-half 01 the disc. The disc is rotated at such a speed that ehe exploration of each section (and therefore the exploration 01 the whole area) takes place whilst the disc is rotating through an angle of 60.

For convenience in description a particular radius 15 of the disc will be taken as a reference member, this radius being one through the magnetizing-coil 12 at the instant that the exploration commences. As this radius moves in a clockwise direction, the indiviidual signals received by each of the c0ils 12, 13, 14 will magnetize the disc as it passes under them, thereby producing a record indicated by the line 16. When the radius 15 has advanced through an angle of 60 to the position indicated at 1"I the record formed by the coil 12 will have reached as Iar 'as the beginning 01 the record formed by the coil 13, and similarly for the other two coils, so that a continuous record extending over one-half 01 ehe circumference of the disc will have been formed, such record having been formed during the time occupied by one-sixth of a revolution of t'he disc.

The reading of this record and its transmission to the receiving-station is effeoted by means 01 a reading-coil or search-coil 18 which is situated at any convenient position, for example, near the coil 12, so that as the record is formecl it passes under it. In the arrangement indicated, the reading of ehe record 16 commences when the reference-radius 15 reaches the position 19, and continues whilst the disc is completing a halfrevolution, that is to say, until the reference-radius 15 reaches the position 20. The magnetization of the disc in accordance with the various signals received from the exploring devices induces electrical impulses in the coil 18 which are amplified by any suitable device 21 and transmitted for example by an aerial 22 to the receiving station.

A demagnetizing 001123 supplied with alternating current at any suitable frequency, is preferably provided immediately behind 'che searchcoil 18 so as 110 wlpe out the -reoord a.s soon as it has been read and transmitted, thereby leaving the disc ready to receive another record.

It will be appreciated that as soon as the tailend 24 of the recorcl 16 has passed the coil 12, a second exploration and recording of the signals derived therefrom may be commenced, such record being formed on that half 01 the disc 10 which was idle during the operation already described, and this sequence of operations may be repeated indefinitely.

In the modified construction illustrated in Figure 3, a rotatable magnetic disc 25 is used, and there are mounted adjacent to it a plurality of magnetizing cells 26,. 2'7, 28, 29 four spacecl apart being illustrated. Each o1 these coils is energized through a selenium cell or other light-sensitive body which is used in conjunction with an exploring device for exploring a s'edtion of the view o1 scene to be transmitted. In this case, tl 1e view is divided. into four s'ections.

A reading-coil or search-coil 30 is so mounted that it can be rotated relatively to the disc, and in the example illusqrated it is rotated in the opposite direction to the disc, and a1; a higher speed, say four times that ofthe disc. The search-coil 30 may also carry with ii a. wipingout coil 31 in the manner previously described.

Taking a particular radius 32 for reference purposes, the mode 01 operation of this apparatus will be as follows. When the radius 32 is in the position indicated the making of the record commenoes, and it continues whilst the disc turns through a quarter-revolution, that is to say, until the radius 32 occupies the position 33. At this point the'record will be complete, extending entirely around the circumference of the disc, and the whole of the view or picture will be recorded thereon. The search-coil 30 is rotated in the direction indicated at a high speed, so as to read and transmit the record, and the speed is Conveniently such that the searchcoil makes one complete revolution during thetime in which the radius 32 turns from the position 33 120 the position 34. That is to say the time occupied in thetransmission is somewhat less than the t1me occupied in the recording of the signals, the difference being due so the fact that the disc 25 1s rotating in one direction whilst the search-coil 30 is rotated in the other direction. A complete cycle of operations has thus been concluded, and may be repeated, record'mg taking place during thenext quarterrevolution of the disc and transmisslon during the last quarter.

With thi s apparatus ehe rate at which the signals are read and transmittzed is somewhat greater than four times the rate at which they are recorded, and tl1e light-sensitive cells are operative during only about one-half 01 the total time. The rate 01 transmission of the signals is thereby greater than could be employed using a single light-sensitive cell to explore the whole picture or view which is to be transmitted.

It' will be appreciated that the search-coll ls required to be operative only du1ing alternate revolutions, and this may be arranged in any couvenient fashion. As diagrammatically indicated. this coil may be coupled to the output amplifier through two rotary switches 35, 36 whlch are provided over a part cf their circumference with a contact-strip, and which rotates in the same direction as the coi1 30 but at a slower rate. Each contact-strip bridges a contact Irom the coil 30 and a contact to the output amplifier and by suitably selecting the relative rates oi movement cf the coil 30 and the switches, and the length of the contact-strips, the coil 30 is isolated during each alternative revolution.

A similar arrangement may be used for coupling the coi1s 26, 27, 28 and 29, to their respective lighflsensitive cel1s', the rotaryswitches being indicated by the character 37.

Obviously, however, the imperative periods of these last-mentioned coils may be obtained by adjustment of the exploring dev'ices.

At the receiving station the signals may be used directly to control the variable light source which is ordinarily used in a television receivingstation, or apparatus similar to that above described may be used in the reverse manner, that is to say, a record is impressed upon it at a high speed, and this record is subsequently read in comcurrent sections by various devices, each of which controls its own source of light or equivalent device.

Whilst it is not intended that the records should ordinarily be other than transient it will be appreciated that permanent records cf a view or picture may be made in accordance with this invention, so that they can be transmitted and viewed, or reproduced at the receiving-station and viewed at any subsequent time.

Finally, it is to be understood that the invention is not limited to the particular magnetic recording device hereinbefore described, for various other methods o f recording electrical impulses are available andany such may be used in the manner hereinbefore set forth.

I claim:

1. A method for the transmission of images consisting in exploring simultaneously individual luminous points in difierent portions of an image, recording simultaneously the explored individual lurninous points in the different portions cf the image, sending successively the recorded portions of the image, and reproducing simultaneously the individual luminous points in difierent portions of the image thus sent.

2. The method of television transmission which comprises scanm'ng simultaneously individual points in a plurality of different portions of an i1'nage, recording the 1ight variations from each portion separately, transmitting the separate recordings in succession, and reproducing simultaneously individual points in the separate transmitted recordings.

3. The method of television transmission which comprises scanning simultaneously a plurality of difierent portions of an image, transforming the light variations 013 each portion into electrical variations, recording the electrical variations for each portion separately, transmitting the separate recordings in succession, and reproducing simultaneously individual points in the separate transmitted recordings.

4. The method of television transmission which comprises scanning simultaneously a plurality' of different portions of an image, trans- Iorming the 1ight variations from each portion into electrical variations, recording magnetically theelectrical variations from each portion separate1y, transmitting the separate recordings in sucicession, and reproducing simultaneously individual points in the separate simultaneous recordings.

5. The method of transmitting television signals which comprises simultaneously scanning a plurality cf different sections of an image, recording magnetically the light variations from each section separately, transmitting the recording from each image separately, and. erasinz each recording after each transmlssion.

6. The method of transmitting television signals which comprises simultaneously scanning a plurality of difierent sections of an image, recording magnetically the l'1ght variations from each section separately, transmitting the recording from each image separately, erasing each recording after each transmission, and. again recording als before on the erased records.

7. In a television system, the method cf reproducing an image, which comprises simultaneous1y scanning individual points in a plurality of difierent portions of an image, recording simultaneously the groups cf signals corresponding to each portion, reading the resulting records progressively and in succession, transmitting in succession the signals corresponding to each group,

and reproducing simultaneously individual points in said difierent portions of the image.

8. In a television system, the method of re-.

producing an image, which comprises simultaneously scanning individual points in a plurality cf difierent portions of an image, recording simultaneously, magnetically on metallic records, the groups of signals corresponding to each portion, reading the resulting records progressively and in succession, transmitting in succession the signals corresponding to each group and reproducing slmultaneously individual points in said different portions of the image.

9. In a telev ision system, the method o! re producing an image, which comprises simultaneously scanning individual points in a plurality of difierent portions of an image, recording simultaneously', magnetically on metallic records, the groups of signals corresponding to each portion, reading the resulting records progressively and in succession, erasing the recorded signals from each record following the reading thereof, transmitting in succession the signals corresponding to each group, and reproducing simultaneously individual points in said different portions of the image.

4- 10. In a television system, the method of reproducing an image, which comprises simultaneously scanning individual points in a plurality 01 different portions cf an image, recording simultaneously, magnetically on metallic records, the groups of signals corresponding 130 each portion, reading the resu1ting records progressively and in succession, erasing the recorded signals ously individual points in said different portions 013 the image, and again scanning the image and recording as before the individual points in a plurality of different portions cf the image on the records, the recordings 01 which have been erased, and continuing to read the records, transmit the signals, and reproduce the image as before.

JOHN LOGIE BAIRD. 

